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July 21, 2011 -- Breastfeeding for at least six months appears to reduce the risk of a child developing asthma, new Dutch research suggests. Exclusive breastfeeding offered even more protection, the researchers found.

The link between breastfeeding and asthma risk has been reported before. However, the new study is believed to be the first to link the length of breastfeeding with the number of wheezing episodes a child has later on.

"Children who were never breastfed had almost 50% more risk of wheezing symptoms as compared to children who were breastfed for more than six months," says Liesbeth Duijts, MD, PhD, a researcher at Erasmus Medical Center in Rotterdam, Netherlands.

Children who were breastfed and given other milk and solids early had 20% more wheezing risk than babies who were exclusively breastfed, Duijts found.

"We suggest that longer and exclusive breastfeeding is associated with a reduced risk of asthma-related symptoms compared to children who do not receive any breastfeeding," Duijts tells WebMD.

The study is published in the European Respiratory Journal.

Breastfeeding and Asthma Risk

Duijts and colleagues evaluated more than 5,000 children from the Netherlands. They asked whether the children had ever been breastfed and if so for how long. They also asked when other milk or solids were given.

Parents answered questions about asthma-related symptoms annually when their children were ages 1 to 4.

Of the total, 92.3% of the children had ever been breastfed. Information about the length of time they were breastfed and whether it was exclusive was available for about 80%.

For those children, the median duration of breastfeeding was 3.5 months (half were breastfed longer, half less). About 21% of the children were breastfed exclusively until age 4 months.

Besides the increase in wheezing, children never breastfed had an increased risk of shortness of breath, dry cough, and persistent phlegm during their first four years, compared to children breastfed for more than six months.

The risks for wheezing and phlegm were the strongest.

Breastfed babies who also were given other milk or solids during their first four months also had an increased risk of symptoms compared to children only breastfed, the researchers found. Besides more wheezing, they had more shortness of breath, dry cough, and phlegm.

Exactly why the breastfeeding seems to protect against asthma was not looked at in this study, Duijts says. However, she says earlier studies suggest the protection is due to breastfeeding's favorable effects on the immune system and on the gut.

"According to our data, we suggest that mothers breastfeed their children for at least six months and at least four months exclusively," Duijts tells WebMD. The researchers only looked at exclusive breastfeeding for four months, as the numbers who exclusively breastfed at six months were too low.

The American Academy of Pediatrics recommends exclusive breastfeeding for about the first six months.

While 75% of U.S. babies start out being breastfed, just 43% are still breastfed at six months and only 13.3% exclusively at six months, according to the CDC.

Applicable to American Babies?

The study adds new information to what is known, says Linda Dahl, MD, an ear, nose and throat specialist at Lenox Hill Hospital in New York. "What is interesting about this study is, they talk about the duration of time."

The researchers also found greater benefits when children were breastfed exclusively, she says.

Dahl cares for adults and children with asthma and allergies. She also helps families whose babies have difficulty breastfeeding.

However, Dahl says, it is difficult to say if the findings would apply to the U.S. The population studied may differ in a number of ways from the U.S. population, she says.